What Is Ethernet? Cables, Speeds and How It Works
How Ethernet works, what is inside a frame, speeds from 100 Mbps to 800 Gbps, which cable category you need, Ethernet vs WiFi, PoE, and connection fixes.
Ethernet is the standard way to connect devices with a cable. It is a family of wired networking technologies, defined by the IEEE 802.3 standards, that carries data between computers, game consoles, TVs, printers, routers and switches. When you plug a cable with a wide, clip-locked connector into the back of your computer, that is Ethernet. The same technology, scaled up, links the servers in every data center and a growing share of the electronics inside modern cars.
This guide covers how Ethernet works, what is inside an Ethernet frame, the speeds and standards from 10 Mbps to 800 Gbps, which cable category you actually need, how Ethernet compares to WiFi, Power over Ethernet, ways to get a wired connection without running new cable, and how to troubleshoot a connection that is slow or not working.
Ethernet in One Minute
- What it is: the dominant wired technology for local area networks, standardized as IEEE 802.3.
- What it is not: the internet. Ethernet connects your device to your router or switch. Your internet service is what lies beyond the router.
- Typical home speed: 1 Gbps, with 2.5 Gbps increasingly common. Data centers run 100 to 800 Gbps.
- Maximum copper cable length: 100 meters (328 feet) for a twisted-pair link.
- Why use it: lower latency, steadier speed and better security than WiFi.
A Short History of Ethernet
Robert Metcalfe described Ethernet in a memo at Xerox PARC in May 1973. The name came from the "luminiferous ether", the medium that 19th-century physicists believed carried light, because the network was meant to be a shared medium any station could send on. The first version ran at about 3 Mbps over thick coaxial cable.
In 1980 Digital Equipment Corporation, Intel and Xerox published a 10 Mbps specification (known as DIX), and in 1983 the IEEE standardized Ethernet as 802.3. Early networks used thick coax (10BASE5) and then thinner coax (10BASE2), where every computer tapped into one long cable. The big change came in 1990 with 10BASE-T, which used ordinary twisted-pair telephone-style cabling in a star layout with a hub in the middle. That made Ethernet cheap and easy to install, and it has used twisted pair ever since.
From there, speed rose roughly tenfold every few years: Fast Ethernet (100 Mbps) in 1995, Gigabit Ethernet in 1998 on fiber and 1999 on copper, 10 Gigabit in 2002, 40 and 100 Gigabit in 2010, 400 Gigabit in 2017 and 800 Gigabit in 2024. In 2016 the IEEE also added 2.5 and 5 Gbps speeds that run over existing office cabling. Metcalfe received the ACM Turing Award, computing's highest honor, for inventing Ethernet.
How Ethernet Works
Every device on an Ethernet network has a network interface controller (NIC) with a unique MAC address. Data travels in units called frames. Each frame carries the MAC address of the device it is going to and the one it came from, so switches know where to deliver it.
From shared cable to switched network
Original Ethernet was a shared medium. Every device heard every frame, and only one could transmit at a time. To manage that, devices used a rule called CSMA/CD (carrier sense multiple access with collision detection): listen before sending, and if two devices start at the same moment and their signals collide, both stop, wait a random time, and try again. Hubs kept this shared behavior, which is why large hub-based networks slowed down as they grew.
Modern Ethernet uses switches instead. A switch learns which MAC address sits behind each of its ports by watching the source address of incoming frames, then sends each frame only to the port where its destination lives. Every cable becomes a private link between one device and the switch, running in full duplex (sending and receiving at the same time), so collisions no longer happen. CSMA/CD is still in the standard but is effectively unused.
Frames addressed to everyone (broadcasts) still go to every port. That is how a device finds the MAC address of your router in the first place, using ARP on IPv4 or neighbor discovery on IPv6. The set of devices that share broadcasts is called a broadcast domain, and large networks split it up with VLANs.
Inside an Ethernet frame
A standard Ethernet frame has a fixed structure:
- Preamble and start frame delimiter (8 bytes): a pattern of alternating bits that lets the receiver lock on to the signal, followed by a marker that says the frame is starting.
- Destination MAC address (6 bytes).
- Source MAC address (6 bytes).
- VLAN tag (4 bytes, optional): an 802.1Q tag that says which virtual network the frame belongs to.
- EtherType (2 bytes): what the payload contains. 0x0800 means IPv4, 0x86DD means IPv6 and 0x0806 means ARP.
- Payload (46 to 1,500 bytes): the actual data, usually an IP packet. Shorter payloads are padded to 46 bytes.
- Frame check sequence (4 bytes): a CRC-32 checksum. The receiver recalculates it and silently drops frames that were damaged on the way.
The 1,500-byte payload limit is the familiar MTU (maximum transmission unit) you see in network settings. Some networks enable jumbo frames of around 9,000 bytes for storage traffic, but on the internet 1,500 is the norm. A VPN wraps each packet in extra headers, which is why VPN connections often use a smaller MTU.
Ethernet and IP
Ethernet works at layers 1 and 2 of the OSI model: the physical signal and the local delivery of frames by MAC address. IP works at layer 3 and handles delivery across networks. When your computer opens a website, it puts an IP packet inside an Ethernet frame addressed to your router's MAC address. The router strips the Ethernet frame, uses network address translation to replace your private IP with your public IP, and sends the packet on over whatever link your ISP uses. MAC addresses never leave your local network. The public IP is the only address a website sees.
Ethernet Speeds and Standards
Ethernet standard names follow a pattern. In 1000BASE-T, 1000 is the speed in Mbps, BASE means baseband signaling, and T means twisted pair. Letters such as SR, LR and SX mean different kinds of fiber. The speeds you are likely to meet:
- 10BASE-T (10 Mbps, 1990): historic. You will only see it on very old equipment.
- 100BASE-TX, Fast Ethernet (100 Mbps, 1995): still found on cheap IoT devices, older printers and some TVs.
- 1000BASE-T, Gigabit (1 Gbps, 1999): the standard on nearly every computer, console and router today.
- 2.5GBASE-T and 5GBASE-T (2016): multi-gig speeds that run over existing Cat5e and Cat6 cable. Common on newer motherboards, WiFi 6 and 7 access points, and routers for multi-gig fiber plans.
- 10GBASE-T (10 Gbps, 2006): workstations, NAS devices and home labs. Needs Cat6a for a full 100 meters.
- 25, 40, 100, 400 and 800 Gbps: data centers and network backbones, almost always over fiber or short copper direct-attach cables.
Both ends negotiate the fastest speed they share. A 2.5 Gbps laptop on a gigabit router port runs at 1 Gbps, and a gigabit connection to a 500 Mbps internet plan is limited to 500 Mbps by the plan.
Ethernet Cables: Which Category Do You Need?
Twisted-pair Ethernet cable contains four pairs of copper wires, each pair twisted to cancel interference, and ends in an 8-pin connector commonly called RJ45. Cables are graded by category:
- Cat5: rated for 100 Mbps. Obsolete, and worth replacing if you find it.
- Cat5e: 1 Gbps at 100 meters, and 2.5 Gbps in most real installations. Fine for most homes.
- Cat6: 1 Gbps at 100 meters, 5 Gbps comfortably, and 10 Gbps up to about 55 meters. The practical choice for new home wiring.
- Cat6a: 10 Gbps at the full 100 meters. The choice for offices, new builds and anyone planning for multi-gig.
- Cat7: not a recognized category in the main North American standards and designed for different connectors. Many cables sold as Cat7 with RJ45 plugs perform no better than Cat6a.
- Cat8: 25 or 40 Gbps over at most 30 meters, designed for data center racks. Pointless for a home.
A few other details matter more than the category printed on the jacket:
- Length: a copper link is limited to 100 meters, conventionally 90 meters of fixed cable in the walls plus 10 meters of patch cords. Beyond that, add a switch or use fiber.
- Solid copper, not CCA:cheap cables made from copper-clad aluminum (CCA) break easily, run hot with Power over Ethernet, and often fail to reach their rated speed. Look for "solid copper" or "pure copper".
- Solid vs. stranded: solid-core cable is for runs inside walls, stranded cable is for flexible patch cords.
- Shielded vs. unshielded: unshielded twisted pair (UTP) is fine for homes. Shielded cable helps near heavy electrical interference, but only if it is grounded properly at both ends.
- Crossover cables are history: modern ports detect the wiring automatically (Auto MDI-X), so any standard cable works between any two devices.
Fiber Ethernet
For longer distances and higher speeds, Ethernet runs over fiber optic cable. Multimode fiber (OM3, OM4) covers a few hundred meters inside buildings and data centers, and single-mode fiber (OS2) covers kilometers. Equipment uses plug-in transceivers (SFP, SFP+, QSFP) so the same switch can take different fiber types. Fiber is immune to electrical interference and lightning-induced surges, which is why it is used between buildings.
Ethernet vs. WiFi
Both connect you to the same LAN and the same internet connection. They differ in how reliably they do it:
- Latency: Ethernet adds well under a millisecond. WiFi typically adds a few milliseconds and, more importantly, jumps around when the air is busy. For gaming and video calls, the consistency matters more than the average. See how to reduce ping.
- Speed: a gigabit Ethernet link delivers close to 1 Gbps all the time. WiFi can advertise higher peak numbers but real throughput falls with distance, walls and the number of devices sharing the channel.
- Stability:Ethernet does not suffer from interference from neighbors' networks, microwave ovens, or thick walls.
- Security: to join a wired network, someone needs physical access to a port. WiFi can be reached from outside your walls, so it depends entirely on encryption and a strong password.
- Convenience: WiFi wins easily. Phones, tablets and laptops that move around should use WiFi.
The practical rule is to wire anything that stays put and needs consistency: desktops, game consoles, streaming boxes, NAS devices, work-from-home setups, and WiFi mesh nodes (a wired link between mesh nodes, called Ethernet backhaul, makes a whole-home mesh far faster).
Power over Ethernet (PoE)
Power over Ethernet sends electrical power down the same cable as the data, so a device needs only one cable. It is what powers most security cameras, WiFi access points, office desk phones and many smart-building sensors. The standards:
- 802.3af (PoE): up to 15.4 W from the switch. Desk phones and simple cameras.
- 802.3at (PoE+): up to 30 W. Most access points and pan-tilt cameras.
- 802.3bt (PoE++): up to 60 W (Type 3) or 90 W (Type 4). Large access points, displays and small computers.
The power comes from a PoE switch or a small inline injector. Budget matters: a switch may advertise PoE on every port but only have enough total power for a few high-draw devices at once. PoE is another reason to avoid CCA cable, which heats up under load.
Getting Ethernet Without Running New Cable
If running a cable to a room is impractical, three options carry an Ethernet connection over wiring you already have:
- MoCA adapters use the coaxial TV cable found in many homes, especially in North America. MoCA 2.5 delivers up to 2.5 Gbps with low latency and is usually the best of the three.
- Powerline adapters (HomePlug AV2 or G.hn) send data over electrical wiring. Results vary widely with the age and layout of the wiring, and adapters work best plugged directly into a wall socket rather than a power strip.
- Existing phone wiring can carry Ethernet using G.hn adapters built for phone lines.
All of them still beat weak WiFi at the far end of a house for consistency, and all of them present a normal Ethernet port at each end.
Ethernet Beyond the Home
- Data centers: servers connect at 25 to 100 Gbps, and the switch fabric between racks at 400 to 800 Gbps.
- Carrier and metro Ethernet: telecom providers sell Ethernet links between business sites across a city, the backbone of many metropolitan area networks and WANs.
- Cars: automotive Ethernet runs over a single twisted pair (100BASE-T1 and faster) and increasingly replaces older in-car networks for cameras, driver assistance and infotainment.
- Factories and buildings: industrial Ethernet variants run production lines, and single-pair Ethernet (10BASE-T1L) can reach sensors up to a kilometer away.
Troubleshooting an Ethernet Connection
- No lights on the port: there is no physical link. Reseat both ends, then try another cable and another port on the router or switch. A port that stays dark with a known-good cable may be disabled in the operating system or faulty.
- Connected at 100 Mbps instead of 1 Gbps: 100 Mbps uses two wire pairs and gigabit needs all four. One broken pair, often from a crushed cable or a badly crimped connector, drops the link to 100 Mbps. Check the negotiated speed (Get-NetAdapter in PowerShell, ethtool on Linux) and replace the cable.
- "Ethernet doesn't have a valid IP configuration": Windows reached the router but did not get an address from DHCP. Restart the router, then run ipconfig /release and ipconfig /renew. The router IP guide helps you reach the router's settings if DHCP is turned off.
- Slow or erratic speed: look for a duplex mismatch (one side forced to a fixed speed while the other auto-negotiates), a cheap CCA cable, a run longer than 100 meters, or an old 100 Mbps switch somewhere in the chain.
- The whole network freezes when a cable is plugged in:a cable connecting two ports on the same network can create a loop that floods it with broadcasts. Managed switches prevent this with Spanning Tree Protocol. On basic switches, unplug the extra cable.
- Connected, but websites do not load: the cable is fine, and the problem is further up. Test name resolution with the DNS lookup and check your public IP and ISP with an IP lookup.
Ethernet Security
A wired network is harder to reach than WiFi, but not immune:
- Unused wall ports: in offices, a live port in a meeting room is an open invitation. Disable ports that are not in use, or require 802.1X authentication before a port will pass traffic.
- ARP spoofing: a device on the same network can pretend to be the router and intercept traffic. Managed switches offer protections such as dynamic ARP inspection, and HTTPS keeps intercepted traffic unreadable.
- Segmentation: VLANs keep cameras, smart devices and guest ports away from computers that hold sensitive data.
- Physical access: anyone who can reach a switch or plug into a cable run can capture traffic. Keep network equipment in a locked space where possible.
For the techniques attackers use once they are on a network, see how hackers steal data.
Frequently Asked Questions
What is Ethernet in simple terms?
Ethernet is the technology behind wired network connections. A cable connects your device to a router or switch, and Ethernet defines how data is packaged and sent over that cable. It is the wired counterpart to WiFi.
Is Ethernet faster than WiFi?
Usually, in the ways that matter. A wired connection delivers its full speed consistently with very low latency, while WiFi speed drops with distance, walls and interference. The newest WiFi can match gigabit Ethernet on paper close to the router, but Ethernet is still more stable.
Is Ethernet the same as the internet?
No. Ethernet connects your device to your local network, usually your router. The internet is the service your router reaches through your ISP. If Ethernet works but the internet does not, the problem is at the router or ISP, not the cable.
What Ethernet cable do I need?
For most homes, Cat5e or Cat6 handles gigabit and 2.5 Gbps speeds. Choose Cat6a for new wiring if you want 10 Gbps over long runs. Avoid copper-clad aluminum cables, and do not pay extra for Cat7 or Cat8 for home use.
What is the maximum length of an Ethernet cable?
100 meters (328 feet) for a twisted-pair copper link. Within that limit, length does not reduce speed. Beyond it, add a switch in the middle or use fiber.
Is Ethernet more secure than WiFi?
Yes, because an attacker needs physical access to a port or cable rather than just being within radio range. It is not a replacement for encryption: use HTTPS and secure apps on any network.
Why is my Ethernet only 100 Mbps?
Most often, a damaged cable or connector with one of the four wire pairs broken, which forces the link down to 100 Mbps. It can also be an old switch or router port that only supports Fast Ethernet. Replace the cable first, then check each device in the chain.
